Public switched telephone networks have served subscribers by transporting telephone signals between a central office and customer premises equipment using a subscriber loop, also referred to as the local loop. The local loop is composed of wires, poles, terminals, conduits, and other outside plant equipment that connect customer premises equipment to the central office of the local exchange carrier. The distance that a copper subscriber loop can be extended from a given central office, known as the carrier serving area, has generally been limited to a range between 9,000 and 12,000 feet. Thus, subscribers within 9,000 feet of the central office can be connected thereto directly via copper POTS lines.
Digital loop carrier systems have been developed to extend the traditional narrowband services such as POTS and ISDN beyond 9,000 feet for a given central office. In digital loop carrier systems, such as subscriber loop carrier (SLC) systems, bidirectional communication usually occurs between a central office (e.g., a local digital switch) and a remote terminal located somewhere between the central office and the vicinity of a customer's premises. Information is transferred between the central office and the remote terminal according to Bellcore TR-008 and TR-303 interface standards using optical fibers carrying 64 kb/s encoded digital channels multiplexed on an optical transport, for example an OC-3 SONET transport. The remote terminal includes optical to electrical interfaces for converting the OC-3 signal from the incoming optical fiber into an electrical signal, and a time slot interchange (TSI) for demultiplexing the 64 kb/s digital channel to telephone line cards. Each telephone line card is configured to serve up to four separate subscriber loops, according to either POTS or ISDN protocol, by respective copper pairs supplying two-way telephone signals to respective subscriber premises equipment.
Digital loop carrier infrastructure can be used to provide various enhanced services, for example, communication of broadband data for multimedia or video services. A portion of the OC-3 transport capacity of the optical fiber between the central office and the remote terminal can be reserved for broadband data, with optical fiber interconnection between the remote terminal and an adjacent remote terminal. Alternatively, a fiber may be run from the central office to the second remote terminal direct from the central office. The second terminal may contain asymmetrical digital subscriber line (ADSL) modem cards. The broadband data can be passed via the second optical fiber, e.g., from the first remote terminal (having telephone line cards), to the second remote terminal (having ADSL modem cards) to modulate the broadband data onto the subscriber loops using the corresponding ADSL modems.
Copending application, Serial Number 09/138,406, filed Aug. 24, 1998 which is incorporated by reference herein, discloses a digital loop carrier remote terminal in detail. FIG. 1 is a simplified block diagram indicative of a network in which such a remote terminal may find use as a multichannel information distribution system for supplying communication between a central office and subscribers in a digital loop carrier serving area. The distribution system provides communication services between a central office (CO) 12 and subscriber premises equipment 14 and 15 without the necessity of a direct connection therebetween. Central office 12 may also serve nearby subscriber premises equipment 16 by direct connection of twisted wire pair lines 18 to a subscriber loop interface, or subscriber line card, within the central office. Remote terminal 20 is connected to central office 12 by a set of optical fibers 24 that carry digitally multiplexed voice channels transported, for example, using a SONET bidirectional OC-3 rate. Subscriber premises equipment 14 and 15 are connected to the remote terminal by twisted pair lines 22 and 22', respectively.
The remote terminal 20 includes multiplexing capabilities for establishing a two-way telephone connection for each subscriber premises telephone equipment by selectively outputting the narrowband data received by the remote terminal 20 to and from the optical fibers 24 and the appropriate twisted wire copper pair connection forming the subscriber loop 22 or 22'. The remote terminal 20 also includes subscriber line circuits for logically connecting the subscriber loop 22 or 22' to a selected one of the narrowband data channels transported by the optical fibers 24.
The system has the capability of serving subscribers with enhanced telephony and broadband services, for example video on demand, or high-speed access to data networks such as the Internet, as well as standard telephone POTS services. Subscriber premises 14 is illustrative of standard POTS service provisioning. Subscriber premises 15 exemplifies use of a conventional telephone as well as a data terminal, such as a personal computer (PC) having an Internet web browser, or a digital entertainment terminal (DET). The DET can communicate with a video dial tone network configured for generating upstream control signals to a broadband information service provider (ISP), and for decoding broadband data received via the corresponding subscriber loop 22' from the broadband ISP. This network communication path includes ATM switch 27 and fiber optic line 26 to the remote terminal. Reference is made to the above-identified application for a detailed description of the remote terminal and operation in a system such as shown in FIG. 1.
A variety of remote terminals are in use in the public switched telephone network, many of which are more simplified than the above described example. Remote terminals generally are enclosed structures, located on site, within which equipment resides for performing any of a wide array of communications. Such equipment may typically comprise a remote line unit, remote line switch, remote line concentrator, and the like. Monitoring of remote terminals or hubs is necessary so that faults can be determined and corrected. Avoidance of the need for frequent on site attendant testing is achieved through remote monitoring. For this purpose, remote terminals are generally provided with analog sensors that generate alarm signals indicative of any of various failures, such as power failure, a physical breach of the terminal enclosure (such as an open door), etc. Alarm signals are also generated for excessive environmental conditions, such as heat, temperature and battery power.
Transmission of alarm signals from a plurality of remote terminals to a maintenance station at a centralized location permits simultaneous surveillance of the remote terminals without the need for an attendant's presence at each remote location. Commercially available monitoring units, such as Hercules, CHATLOS, Spartan, and the like, placed on site, enable dial up to the centralized location in response to a generated change of state alarm signal at the remote terminal. Analog sensors change the state of contacts in a dc loop that is connected to a respective port in the monitoring unit. For each condition sensed, each remote monitoring station transmits a data message, typically in ASCII format, to the centralized maintenance station, which is printed on one line of a printer. The message includes, among other information, the address of the sending station and the alarm status condition.
FIG. 2 is a simplified block diagram of a prior art network remote terminal monitoring system, as described above. A plurality of remote monitoring stations 30 are located at corresponding remote terminals and linked through the public switched telephone network to centralized maintenance facility 50. Modem 52 at the facility permits receipt of data messages from stations 30, which messages are printed as received at a printer 54.
The large volume of alarm signal printouts imposes a burden on the maintenance station, as at least one clerk must almost constantly go through all the printout pages and make decisions as to how to deal with the alarms. Further complicating the situation is the fact that every alarm status change in the remote terminal, whether from alarm on to alarm off or vice versa, generates an alarm signal transmission. For example, opening of a door in the remote terminal unit would generating an alarm on status signal and closing the door would generate an alarm off status signal. The clerk must often go through needless perusal of printout data just to determine that alarm on conditions have been cancelled in subsequently received alarm off data messages.
Thus, the need exists for a more efficient way to manage the alarm data received at the centralized station from the various remote terminal monitoring stations prior to the human decision making process. The centralized station should have the capability of readily ordering the received data by source, parameter sensed, and type of alarm condition. It would be highly desirable to have capability to separate out data that is currently of importance for impending corrective disposition from the complete chronological data log that may be retained for historical tracking purposes.